عنوان مقاله [English]
In most cases, faults can be detected by signs; however, in many cases, the outcrops of these structures have not reached the surface of the earth, or deposits have been buried with evidence and indications. Such conditions, although the surface of the earth's crust on both sides of the fault is displaced and drifting up or down, however, the surface out crop of the fault is not observed at the ground or is limited to stacks and mild folds in sections along the fault. To identify these types of faults, geophysical methods, CO2 and soil radon measurements, seismic reflections and electrical imaging, lidar, penetrating ground radar or air geophysics can be used. Researchers who have studied the buried faults of the earth's crust have generally used geophysical methods. According to Giving and colleagues, the results of aerial geophysical data in order to identify hidden faults, if accompanied with evidence of geomorphology and topographic data, have higher scientific value. In this research, the aim is to find hidden faults through geomorphic interpretation methods.
Among the areas where active tectonics and faults have been buried and the river sediments have buried their works, the east of Kermanshah province is in the Harsin and Bisetoon plain. First, geological maps and topography, geomorphology, and geostructral were explored and interpreted. Based on the hypothesis of the separation of the Shirez anticlinal from the nape as one of the geostructural and morphotectonic evidence, and the flow of the Gamasyaw river and the morphology of the Tsetonic plain of Harsin, the overall boundary of the hidden faults was identified and mapped to geology. In the next step, by studying the data of aeromagnetism and the use of return-to-pole filters, vertical derivatives, analytical signal and tilt, a more precise location of the faults was maped. Then, on the 4 main faults identified, 5 sections of VLF As and Mg As were taken and the results of the previous steps were verified using the geoelectric method.
Results and discussion
What is obtained from the results of a total of three methods used to identify hidden faults is a number of faults that have been scattered across the region. The first fault in the almost west to east direction from west of the Taqbostan elevations in the north of Kermanshah plain extends over the Taqbostan elevations, and after passing on the Prao and Bisetoon elevations, with the shift of direction from southwest to northeast to Barnaj, and from there with change the almost east-easterly direction enters the plain and continues in the south of the Khaneh-khode mountain, and after passing through the Sahneh plain, it again extends to the north-east by changing the trend. Between the Bisetoon elevations to the Sahneh plain, 5 faults along the north-south direction extend approximately from the first fault to the shores of the Shirez anticlinal. These faults have been driven by the sliding motion. Another fault that seems to play an important role in the region's morphology and history of geomorphology in the region has started from west of Kermanshah and in the south of the Paro elevations it continues along the southeast to the Harsin plain. Comparison of the results of the three stages of the research showed that what the aeromagnetism and geoelectrics identified as faults, geomorphology, with a small spatial variation, and a negligible distance, as a fault that must exist to justify the region's morphology had identified. Geomorphology is largely capable of treating anomalies and movements caused by faults that are sometimes detected in the field by interpreting geospatial maps and analyzing the geostructural of the area along with simultaneous surveys of geomorphic, topographic, satellite images and remote sensing maps that geologists can not be identified. What is certain is that the effect of hidden faults in the region's morphology is observed only in some areas where the effect of the fault has reached the surface directly and in the expected form; otherwise, in the identification and tracing of the hidden fault by geomorphology, we must look for indirect effects and the effects of long-term faults on morphology, especially geostructural, on a larger scale than the usual methods of morphotectonic studies. It can be said that geomorphology can be successful in finding hidden faults that it has a comprehensive view on geotechnical and past geographic of region. In fact, a thorough examination of the geomorphological nature of the forms is based on the interpretation of the function of the faults, in particular the hidden faults, which themselves sometimes lead to the finding of hidden faults.